The present invention relates to automatically managing the delivery of digitally compressed visual data, and more particularly, to a device and method for controlling the bitrate and error robustness of digitally compressed video bitstreams in a heterogeneous communications network.
With the advent of new communication systems, it has become possible to communicate digital visual information and data in addition to just voice services efficiently. Such new communication systems comprise both wireline and wireless networks. In the context of wireline networks, packet and circuit switched communication systems have been developed in both the private and public domains for wide and local area coverage. As part of packet-based communications, a significant amount of data is exchanged between local area networks, such as those which are part of a corporate infrastructure, and wide area networks, such as the public Internet. Services to guarantee Quality of Service (QoS) have emerged in this realm to support visual and multimedia communication.
New wireless systems have also been developed to support the transmission of information at higher bitrates than previously possible. These wireless systems conform to international cellular communication standards, and consist of digital communication air-interface standards using Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA). An example of widely deployed TDMA communication is the Global System for Mobile communication (GSM). CDMA forms the basis for the third generation cellular communication standard IMT-2000.
Most of these communication systems (wireline and wireless) have been designed to allow for the exchange of a maximum amount of information between users connected within the infrastructure of each system and those using devices outside that infrastructure. For example, IMT-2000 protocols can support data communication from wireless terminals to terminals residing on packet switched wireline systems. Moreover, within these communication systems, terminals, or clients, may connect to other terminals, acting as servers, at different bitrates depending on their location in each system. This leads to the concept of heterogeneous communication networks, which are networks consisting of diverse or dissimilar connections yet often communicating similar information.
Problems arise when considering the communication of visual information in heterogeneous networks. A first problematic issue which arises is that visual information, and, in particular, digitally compressed video signals, require substantially more bandwidth than comparable voice signals compressed over similar time intervals. Transmitting visual information between systems designed with different nominal transmission bitrates presents some difficulty because of delays that result from these incompatible bitrates. In addition, varying error characteristics of the different communication systems in a heterogeneous network also present a problem for the transmission of visual information because it is very difficult to mask errors in the visual space.
These problems do not alone make up the difficulties with communicating visual information over diverse systems. Services designed to exploit the communication of visual information in heterogeneous networks must, necessarily, rely on the existence of digitally compressed video. Therefore, not only creating new content, but exploiting existing content is a primary focus for the further development and success of these services. For one-way visual applications, there is already a substantial amount of digitally encoded content for training and entertainment that could be delivered to mobile subscribers on a wireless network, or to clients connected at dissimilar rates on a wireline network. Existing, or xe2x80x9clegacyxe2x80x9d video material is primarily encoded using the ISO MPEG-1 and MPEG-2 standards, although legacy content also exists in the form of the ITU-T H.261 and, to a lesser extent, H.263 standards. This material can have high value to new multimedia services, while at the same time lead to the acceptance and use of new visual coding standards such as ISO MPEG-4.
One problem with the delivery of legacy data over the low bandwidth wired and wireless networks is that the original encoded bandwidth typically exceeds the capabilities of the network, assuming that there is a maximum delay restriction on the delivery of that data. For example, some wireless mobile systems may have multimedia terminals supporting MPEG-1 decoding, but the channel rates to the multimedia enabled mobile terminals may be as low as 64 Kbps. In this case, the MPEG-1 material, encoded at 1.5 Mbps, would require substantial buffering delay time before playback could begin. Unless most of the sequence was to be downloaded first, stalling would occur, as the decoder""s buffer would empty much faster than it would fill. It is also unlikely that a mobile terminal would be able to provide sufficient memory for buffering long sequences. A requirement exists, therefore, to successfully manipulate this type of high bitrate data to a lower rate such that it is compatible with a low bandwidth connection on the network.
As a result of the arrival of new wired and wireless communication systems with the capacity to transmit and exchange visual information, there is a significant need for a method and device designed to manage the visual content being delivered over these networks. In particular, technology is needed to automatically manage the bitrate and error robustness of pre-existing digital video bitstreams so that they can be delivered in a compatible form to users at arbitrary nodes in a heterogeneous network.
Briefly, therefore, this invention provides a method and apparatus for changing a digitally compressed video bitstream at a source point in a network, in an automatic way, such that the resulting bitstream is compatible with different bandwidth and error resilience requirements at a receiving point in a heterogeneous communication network. The novel method consists of analyzing the header information of the original bitstream to determine its coding parameters. Feedback from the receiving point on the network is then used to determine error properties of the network. The bandwidth and error resilience requirements establish a prioritization and selection of relevant and irrelevant bits from the original bitstream, of which the relevant bits are manipulated by a robustness regulator to achieve error protection in the network. The principal inventive components of the method include identification of irrelevant and low priority video bits, intentional introduction of packet losses to reduce bitrate, use of replacement tags for irrelevant and low priority components of the bitstream, and insertion of resynchronization tags for the improvement of error resilience.